Lois Wagener has lived on the Aupouri Peninsula long enough to have noticed how Houhora Harbour is changing - and she is deeply concerned that it is in the process of becoming the marine equivalent of a wasteland.

The harbour had been subjected to growing levels of pollution for a number of years, she said, but an increase in intensive cropping and orcharding had greatly accelerated that pollution over recent years. Silt levels had increased markedly within the sand layer along the foreshore, especially at the heads and on the sand banks in the middle of the harbour.

The result had been rapidly growing areas of sea grass, both along the southern shoreline at the heads and on the sand banks in the middle of the harbour.

"The sand banks where the grass is now growing are soft and silty, making it more difficult to walk over what were once firm, clean, sandy banks," Mrs Wagener said.

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"Small mangroves are becoming more common on the sand banks, and indeed around the mouth of the Raio and Motutangi streams. Soft silt-laden sand is now also common in both these locations within the harbour.

"There was a small channel that crossed through the sand banks in the middle of the harbour, which has now completely closed over. It was from the Little Rock to the commercial wharf, approximately, but it is no longer there."

She blamed intensive horticulture, with vast areas of former pasture having been sprayed, ploughed and fertilised for annual crops including maize and water melons, leading to increased the runoff. Once the crops had been harvested the land generally returned to pasture, so further tilling and more fertilising, were needed for the following year's crops, again leading to the loss of soil during rain.

That soil, and excess fertiliser, were finding their way into the harbour.

Mrs Wagener had photographed soil-laden water flowing out the harbour on May 28, after days of heavy rain, and witnessed the same phenomenon earlier this month, again after heavy rain.

"The water flowing from the Motutangi Stream has always been discoloured due to its passage through peat," she said. "But over the last four or five years the composition of the discharge has changed from that similar to a cup of black tea to representing more a cup of muddy water, in which you are not able to see your fingers. The discharge after rain is laden with soil and other particles.

"I, of course have no scientific statistics to support any of my concerns, but I have frequented the harbour for weeks at a time, staying at the heads over the last 54 years. We have lived all but 10 of the last 24 years at Houhora Heads.

"As a keen ornithologist, I am also acutely aware of changes to the sand banks over the last few years because of the decline in shore bird numbers, both observed feeding on the banks and also seen flying between Houhora Harbour and Walker Island in Rangaunu Bay.

"It is time for some form of intervention before the Houhora Harbour dies," she said. "I am aware that people have to make a living from the land, but management of our water resources and our coastal waterways is imperative."